X-ray tube

ABSTRACT

The invention relates to an X-ray tube in which the anode and the cathode are accommodated in two parallel adjacent envelopes which are interconnected by a tubular member through which the electron beam passes. At high voltage (300 kV and higher) the direction of the electron beam and the direction of the maximum of the X-rays are inclined at an obtuse angle to one another. Thus the electrons impinge on the target nearly at grazing incidence. Even at slight deviation of the relative positions of the anode and cathode envelopes from the prescribed positions the focal spot is greatly shifted. According to the invention the two envelopes are relatively movable, causing substantially a deformation of the coupling member only which is capable of deformation owing to the use of an appropriate construction and/or a suitable material.

United States Patent [191 Berends et al.

[ March 6, 1973 X-RAY TUBE [73] Assignee: U.S. Philips York, N.Y.

[22] Filed: Jan. 8, 1971 [21] App1.No.: 104,968

Corporation, New

[30] Foreign Application Priority Data Feb. 25, 1970 Germany ..P 20 08 782.5

[52] U.S. Cl. ..3l3/57, 313/60, 313/148 Primary ExaminerRoy Lake Assistant Examiner-Darwin R. Hostetter Attorney-Frank R. Trifari [57] ABSTRACT The invention relates to an X-ray tube in which the anode and the cathode are accommodated in two parallel adjacent evvelopes which are interconnected by a tubular member through which the electron beam passes. At high voltage (300 kV and higher) the direction of the electron beam and the direction of the maximum of the X-rays are inclined at an obtuse angle to one another. Thus the electrons impinge on the target nearly at grazing incidence. Even at slight deviation of the relative positions of the anode and cathode envelopes from the prescribed positions the focal spot is greatly shifted. According to the invention the two envelopes are relatively movable, causing substantially a deformation of the couplingmember only which is capable of deformation owing to the use of an appropriate construction and/or a suitable material.

1 Claim, 1 Drawing Figure X-RAY TUBE The invention relates to an X-ray tube, in particular a tube for voltages of 300 kV and higher the anode and cathode of which are accommodated in one of two parallel adjacent envelopes, the electron beam'passing from the cathode to the anode through a tube coupling the envelopes. Such an X-ray tube is known. The particular advantage of this construction consists in that it enables the high voltage cables for the anode and the cathode to be brought in from the same side with consequent ease in handling the tube.

In the known X-ray tube use is made of the X-rays which emerge at right angles to the electron beam, and at low tube voltages this provides satisfactory results. However, in the case of high-energy electrons (300 kV or more) the maximum of the radiation energy emitted from the anode makes an obtuse angle with the impinging electrons. The resulting problems will be discussed with reference to the accompanying drawing, which is a schematic diagram of an embodiment of the invention.

The Figure shows a casing l of an X-ray apparatus which contains two grounded envelopes 2 and 3 for the anode 4 and the cathode 5 which are mounted on insulators 6 and 7 respectively which are secured in a vacuumtight manner to the envelopes 2 and 3 respectively and have cavities 8 and 9 respectively for the respective high-voltage plugs. The envelopes 2 and 3 advantageously each consist of a hollow cylinder one end of which is closed by means of a hollow hemispherical member and into the other end of which the respective insulator has been inserted. The two envelopes are interconnected by a coupling tube 10, through which the electron beam passes from the cathode space into the anode space. As has been mentioned hereinbefore, the electron beam 11 and the direction 12 of the maximum of the X-rays make an obtuse angle of, for example, 145 or considering the angle between the imaginary continuation of the electron beam and the maximum an acute angle of 35.

This means that the target 13 in the anode 4 may not be inclined at an angle of more than 45a to the electron beam, since otherwise the X-rays in the direction of the maximum will be absorbed by the target. However, in practice the angle must be even smaller, because the X- rays about the maximum are also to be utilized. If, for example, an X-ray cone which has a vertical angle of 40 and in the axis of the maximum is to permit full utilization of the X-rays, the angle should be only 35 20 15. With so small an angle even the smallest tolerances, which are substantially unavoidable in manufacture, will cause a comparatively large shift of the focal spot.

The invention permits a considerable cancellation of this shift. For this purpose, according to the invention the X-ray tube is designed so that in order to displace the focal spot on the target 13 the envelopes 2 and 3 are capable of relative movement in which substantially only the coupling tube 10 is deformed.

The adjustment made possible by this construction is effected after the assembly of the envelopes, i.e., after the insulators 6 and 7 for the anode 4 and the cathode 5 have been mounted in the envelopes 2 and 3 respectively and after the two halves of the coupling tube 10 have been welded or soldered to one another. Advantageously, the cathode envelope only is moved whilst the anode envelope is fixed so as to prevent a change in its position relative to the X-ray exit window.

The anode envelope may be secured, for example, by bolts, not shown, which draw a flange 15 of an anode insulator 6 against a mounting plate 17 which is welded to the casing l and has openings for receiving the anode and cathode envelopes, until a flange l8 welded to the envelope 2 is firmly pressed against the mounting plate 17 throughout its entire surface area.

The cathode envelope 3 is best adjusted with the high voltage switched on so that the location of the focal spot on the target 13 may be checked through the X- ray exit window; the means of adjustment are not shown in detail.

When the electron beam does not impinge at the intended point in the direction at right angles to the plane of the drawing, a correction may simply be effected by slightly rotating the cathode envelope 3 about its axis. When the electron beam impinges at too high or too low a point, the required adjustment may be performed by tilting the cathode envelope (with respect to its central axis). For this purpose three bolts may be used which are mutually displaced at angles of and press against the envelope 3 in radial directions at the level indicated by the arrow 20 and may be tightened by means of screwthread formed in the casing 1. By suitable tightening of the three bolts the cathode envelope together with the cathode may be tilted to the left or to the right, enabling the electron beam and hence the focal spot to be shifted upwardly or downwardly respectively. To prevent the adjustment from being lost when the flange 16 secured to the cathode insulator 7 is secured in position, there may be provided in a flange l9 welded to the envelope 3 bolts which are screwed against the mounting plate 17 so that the flange 19 bears on the mounting plate 17 at several points and the adjusted relative positions of the two envelopes are maintained. The deformation of the coupling tube 10 alone due to the adjustment is obtainable by the use of a suitable material, by the choice of the wall thickness or by appropriate shaping. For example, the coupling tube 10 may be a concertina or bellows.

In an embodiment of the invention the said properties are obtained in that the coupling tube 10 comprises two halves 10a and 1012 which are welded to the envelopes 2 and 3, respectively, and are flanged over at the ends facing one another and are joined to one another by butt welding.

However, the use of the invention is not restricted to tubes of metal-ceramic construction but it may also be used for X-ray tubes of known metal-glass construction in an appropriate insulating medium.

What is claimed is:

1. An X-ray tube including a base, an X-ray exit window, an anode and a cathode comprising a pair of envelopes open at one end and having side walls adjacent and substantially parallel to each other, one of said envelopes being positioned around said anode and the other of said envelopes being positioned around said cathode, a deformable sleeve interconnecting adjacent portions of said side walls of said pair of envelopes and forming a continuum of space from said one of said envelopes to the said other of said envelopes whereby an electron beam can pass therethrough from said cathode to said anode, a target disposed within said anode and having at least one flat surface positioned with respect to the angle of incidence of said electron beam at less a respective one of said pair of insulators, whereby said electron beam can be directed to a spot on said flat surface which directs substantially all of said X-rays out of said X-ray exit window upon said insulator supporting said cathode being tilted and said deformable sleeve adjusting elastically to prevent movement of said flat surface. 

1. An X-ray tube including a base, an X-ray exit window, an anode and a cathode comprising a pair of envelopes open at one end and having side walls adjacent and substantially parallel to each other, one of said envelopes being positioned around said anode and the other of said envelopes being positioned around said cathode, a deformable sleeve interconnecting adjacent portions of said side walls of said pair of eNvelopes and forming a continuum of space from said one of said envelopes to the said other of said envelopes whereby an electron beam can pass therethrough from said cathode to said anode, a target disposed within said anode and having at least one flat surface positioned with respect to the angle of incidence of said electron beam at less than an angle of 35*, a pair of insulator supports disposed on said base, a pair of insulators each disposed within one of said pair of envelopes and mounted each on one of said insulator supports, one of said pair of insulators supporting said cathode and the other of said pair of insulators supporting said anode, said one of said insulators supporting said cathode being tiltably mounted on said insulator support, each of said pair of envelopes being sealingly connected at its open end to a respective one of said pair of insulators, whereby said electron beam can be directed to a spot on said flat surface which directs substantially all of said X-rays out of said X-ray exit window upon said insulator supporting said cathode being tilted and said deformable sleeve adjusting elastically to prevent movement of said flat surface. 